Middle Eastern conflicts always unfold on multiple levels — think 3-D chess — and for Israel the most relevant level of the crisis in Syria is what it says about the world’s approach not to Syria, but to Iran. As the U.S. prepares to make good on its threats to launch military strikes punishing the government of Syrian President Bashar Assad for its alleged use of chemical weapons, Israel sees the situation as a test of international resolve on checking Iran’s nuclear ambitions, which Israel’s leaders call an existential threat.

“The Iranians are watching very closely how we respond,” says an Israeli official in Jerusalem. “The implications of this go beyond Syria.”

Yet at ground level, Syria is awfully close to Israel proper, and ordinary Israelis have reason to worry that an American air strike could produce consequences beyond the theoretical or geopolitical. Syrian forces stand just across 47 miles (76 km) of Israel’s northern frontier, and its ally Hizballah roams the grassy highlands of southern Lebanon that account for the remaining 49 miles (79 km). The former apparently has used chemical weapons on its own people, and the latter rained thousands of rockets into Israeli cities and towns just seven years ago.

In the mind of the Israeli public, those memories combine against the assurances of Israeli leaders that Damascus is unlikely to strike out at Israel in response to the expected American air strikes. The policymakers’ assessment is based on monitoring of Assad’s military, which betrays no preparations to carry out the retaliation threatened by midlevel Syrian officials, whose bellicose rhetoric is judged chiefly for domestic consumption.

But cool calculation was not what drove the Jerusalem residents who overwhelmed a gas-mask distribution center at a shopping mall Thursday, forcing it to shut down early. Like the long lines extending at other gas-mask distribution points this week, the episode betrayed the rising unease coursing just below the surface of Israeli society.

“We need masks for our families just like everyone else in Israel,” says Zeinab Sheikha, waiting outside in a Jerusalem distribution center. “If Syria attacks, then none of us are safe.” An Arab citizen of the Jewish state, Sheikha sat beside a religious Jewish woman. One wore the headscarf of a pious Muslim woman, and the other, the headscarf of a religious Jewish woman — strikingly similar except for the way the fabric is tied.

“We’ll prepare as best we can, to the extent we can, just in the way we did in 1990 for the Gulf War,” says Tzipi, the Jewish woman (who said she could not give her last name because as an Education Ministry employee she is not authorized to speak to the media). In 1990, Saddam Hussein threatened to strike Israel with chemical weapons in retaliation for U.S. military actions to drive the Iraqi army out of Kuwait — a situation with just enough parallels to the Syrian situation to galvanize attention anew. Hussein never did use chemical weapons against Israel, using conventional Scud missiles instead, but the uncertainty was terrifying in itself, given Iraq’s history of poison gases used against Iranian forces and Iraq’s Kurdish minority.

“We got everything ready, and the worst never materialized,” Tzipi recalls. In comparison, she says, consider the Yom Kippur War in 1973, when Israel was largely surprised and suffered heavy battlefield losses. It went down as a dark chapter in Israeli military history. “We never want to leave ourselves in that situation again,” Tzipi says, “so we prepare and even overprepare.”

In the current crisis, Israel’s calculations are muddied by Syria’s recent behavior. Though technically still in a state of war with Syria by dint of hostilities that date back to Israel’s 1948 founding, for decades the neighbors have maintained a practical stability in many ways almost as predictable as with Jordan and Egypt, neighbors that signed peace treaties. Israeli policymakers regarded Assad as a rational if ruthless leader whose actions were guided by his interests. After Israeli jets secretly bombed a nuclear facility in the Syrian desert in September 2007, Israeli leaders declined to take credit for the strike, and Assad, significantly, declined to retaliate.

But the wrenching civil war in Syria, besides claiming more than 100,000 lives, has threatened the existence of Assad’s regime and challenged the traditional calculus of Syrian behavior. The best example is the chemical attack that killed hundreds outside Damascus on Aug. 21, including many children in their beds — if indeed it was the work of the Syrian military. “The Syrians already made a professional — technical and strategic — mistake when they used rockets with chemical weapons in the Damascus suburbs,” defense reporter Alex Fishman wrote in the Israeli newspaper Yedioth Ahronoth Wednesday morning. “The person who made such a mistake is liable to make more mistakes. And that is what the state of Israel is preparing for.”

The preparations are relatively low key. Iron Dome and Patriot antimissile batteries have been moved to Israel’s north, the area most vulnerable to short-range missile fire from Syria and Lebanon. Weekend leaves were canceled for Israeli military units in the area, and reinforcements sent from the south. Only about 1,000 reservists were called up, chiefly to the air force, military intelligence and Home Front Command, the Israeli Defense Forces section responsible for safeguarding the civilian population.

At the same time, the office of Prime Minister Benjamin Netanyahu ordered Israeli officials to refrain from commenting on Syria, emphasizing the importance Israel maintains on keeping out of things, at least publicly. The Jewish state remains a pariah in much of the Arab world, handy for any party seeking to change the subject. “We’re situated in proximity to an American operation and we view this as an entirely American affair,” the Hebrew daily Ma’ariv quoted an Israeli military official as saying. “Israel’s involvement is being discussed only because it’s Syria’s neighbor.”

In fact, the Israeli military and the Pentagon work very closely as a matter of routine — the chief of staff of the U.S. Air Force spent four days in Israel earlier in August — but U.S. military personnel were maintaining a very low profile inside Israel this week, Israeli military sources tell TIME. The discretion was partly because Israel is not being called upon to take part in the strikes the U.S. is planning — which the Israelis gather will involve only cruise missiles, so as not to endanger U.S. pilots — and partly because Washington prefers to emphasize the support for the strikes from other quarters.

Intelligence continues to be shared between Israel and the U.S., however, including communications intercepts down the chain of command that showed the chemical attack had been ordered by Assad’s forces, an Israeli military official tells TIME. “Both Americans and Israelis have enough information about the Syrian regime involvement in the chain of command,” the Israeli military official says.

Karl Vick has been TIME's Jerusalem bureau chief since 2010, covering Israel,the Palestine territories and nearby sovereignties. He worked 16 years at the Washington Post in Nairobi, Istanbul, Baghdad, Los Angeles and Rockville, MD.